Coating sheet material



Aug. 12, 1941- 5. J. JOHNSON 2,252,345

COATING SHEET MATERIAL Filed June 11, 1938 Fig: 5.

Patented Aug. 12,1941

COATING SHEET MATERIAL Stanley J. Johnson, Portland, Maine, minor to S.D. Warren Company, Bosto n, Man, I 001'- poratlon of MassachusettsApplication June 11, 1938, Serial No. 213,275

14 Claims.

This invention relates to methods of and apparatus for coating sheetmaterial. The invention is applicable to the coating of woven or feltedfabrics, paper, sheets of rubber or other resinous material, films ofregenerated cellulose or of cellulose esters or ethers, and other sheetmaterial of similar nature.

A widely used method of coating flexible-sheet material is thatdisclosed by Lebel in U. S. Patent No 1,980,923. That method, in brief,comprises applying a fluid coating composition to one side of a flexibleweb, and then supporting the reverse side of the coated web while it iscarried past an air jet or air brush" which extends across the width ofthe web and is directed at the coated surface directly opposite thepoint of support;

The air jet smooths the layer of fluid coating composition. It mayactually cut away part of the coating, which has been applied in excess,

leaving a predetermined residual quantity which it redistributes, evensand smooths on the web in a uniform layer. This method yields a veryexcellent coated product but it is limited to coating only one side ofthe web at a time, owing to the fact that the back of the web must besupported while th air jet is acting on the freshly coated side. Thesmoothing of a coating by means of an air jet without the use of rigidmeans for supporting the web against the jet is not regarded as feasibleat present. Otherwise it would be a simple matter to coat both sides ofa web and then smooth both sides in a single pass by means of air jets.The use of one air jet as the supporting means for another air jet alsois not regarded as being feasible at present.

By coating only one side of the paper at a time I mean coating only oneside of the paper in a single pass of the web from a source such as areel, through the coating operation and a drying operation.

Another method of coating paper which is ca-- pable of yielding anexcellent coated product is one in which fluid coating composition issmoothed on the surface of the web by a driven roll which contacts thecoated surface with a wiping action. In this method the coating may be,both applied to and smoothed upon the web ing the web around it undertension.

per in contact with the smoothing roll by bend- In such a case it ispractically necessary that the paper shall have a considerable arc ofcontact with the smoothing roll in order to insur that every spot on thepaper surface shall actually be contacted. Otherwise skips or unevenspots may occur on the coated surface. Thus it is seen that there isunavoidable a considerable frictional drag on the paper, since thelatter must be held firmly against the roll but yet at the same timemust slip over a considerable portionof the roll surface. Nevertheless,paper of fair strength can be smoothed or coated and smoothedsatisfactorily by this method, particularly if the pull between thesmoothing roll and the first succeeding tension means is comparativelyshort. It

by the wiping roll or it may be applied in some would appear feasible,and it has been proposed, to coat and smooth both sides of a web in asingle operation by using two such wiping or smoothing rolls withoutbacking rolls placed on opposite sides of the web one ahead of the otherso that both rolls do not contact the web at the same point. It isapparent, however, that such practice doubles the frictional drag on thepaper and consequently, while it is possible to carry out the methodexperimentally in the case of strong paper, the method has not proved tobe generally practicable for production use at ordinary commercialoperating speeds. Hence, for practical purposes, roller-coating of thisnature still remains a one-side coating process. Coating both sides ofthe web in a single pass by providing smoothing rolls on opposite sidesof the web, each holding the web against th other is, so far as I amaware, not practically possible with equipment available at present.

The two comparatively new coating methods, 1. e., the air brush methodand the roll-coater method, are both generally considered to yieldcoated paper of a quality superior to that produced by the older, doublebrush-coaters of conventional type. Moreover, both new methods arecapable of operating at considerably higher speedsthan the oldbrush-type coaters can attain. Consequently the newer types of coatersapplied as one-side coaters are able to, and do,

compete successfully with the older type doublecoaters. It is apparent,however, that a modification of either the air brush method or therollcoater method or some combination of them which would achievesatisfactory coating of both sides of the web in a single operation andat the speeds now commonly used for those methods in one side operation,would result in an advantageous increase in speed of production with acorresponding decrease in production cost. The present inventionaccomplishes this desirable result.

It is an object of the present invention to provide improvements inmethods of manufacturing sheet material coated on both sides in a singleoperation.

Another object is to provide a method of coating sheet material on bothsides in a single operation which involves the use of two rectilinearsubstantially non-divergent air jets.

Another object is the provision of a method of holding a web of sheetmaterial bearing a layer of mobile coating composition against a rigidsmoothing device by means ofair pressure.

Another object is the provision of a method of holding one side of a webof sheet material bear-- ing a coating on both sides against a rigidsmoothing device by means of an air jet which also serves to smooth theother side.

Another object is to provide, in a method of coating sheet material onboth sides in a single operation, the improvement comprisingsmoothingthe coating on one side by means of an air jet and on the other side bymeans of a roll, the air jet serving to hold the web against the rolland the roll serving to support the web against the Jet.

Another object is to spread coating on one side of a sheet by an air jetand on the other side by a rigid scraper or blade.

Another object is to provide new combinations of apparatus for theaccomplishment of the aforesaid objects.

Other objects and advantages will appear hereinafter.

Broadly, the invention resides in the use of an air jet for holding acoated web of sheet material against a rigid device, either a roll orscraper, which serves to smooth the coating and may also serve to applycoating and more specifically the rigid device may also serve to supportthe web against the air jet while the latter serves to smooth a coatingon its side of the web.

The coated sheet is dried in any suitable manner, as on an air-floateror in a tower or tunnel and the sheet is then finished as desired.

Fig. 1 is a diagrammatic showing of the essential parts of oneembodiment of the invention.

Fig. 2 is a diagrammatic showing of a second embodiment of theinvention.

Fig. 3 is a diagrammatic showing of a modification of the apparatusillustrated in Fig. 2 in which the scraper 2| of Fig. 2 is replaced by aroller.

Fig. 4 is a diagrammatic showing of a portion only of the apparatusillustrated in Fig. 1 in which the air jet I0 is replaced by a roller.

In Fig. 1 a web for example a web of paper, with its two sides indicatedas A and B respectively, is unwound from reel 2, passed over guide andtensioning rolls 3, 3 and passed with side A in contact with roll 4which turns in a' vat 5 containing fluid coating composition. Roll 4 isdriven, by means not shown, at a speed which permits the application ofthe web of the desired weight of coating composition, usually an amountsomewhat in excess of that desired on the finished paper. The web thenpasses with side B, in contact with guide-roll 6 and past air-nozzle lwhich emits a rectilinear, substantially non-divergent jet of airagainst coated side A, thus smoothing the coating on side A and removingthe excess coating, if any. Roll I, contacting side 3 of the web, actsas a backing-roll to support the sheet while the air jet from nozzle iiis acting on side A. Roll i also carries a film of coating compositionwhich it transfers to side 3 oi the web at the point of contacttherewith. Fluid coating composition is applied to roll l, preferably inexcess, by roll 8 which turns in vat d, containing the coating mixture.The coating on roll 'l is spread and smoothed, the excess if any beingremoved in the process, by a rectilinear, substantially non-divergentair jet from nozzle iii. The web, now coated and the coating spread andsmoothed on both sides, is carried to a suitable drier E2 in which thecoating is dried sufiiciently not to be marked before it contacts guideroll l3. The web is dried further in its passageto guide-roll i i, andis then wound up on reel l5.

Air-nozzles i0 and II may be constructed according to the disclosure ofthe co-pending application of K. E. Terry, Serial No. 78,235, now PatentNo. 2,139,628. In the above described embodiment any suitable means maybe substituted for roll 4 for applying coating to side A of the web andinstead of applying coating to the side B of the web by means of roll I,coating may be applied by any other suitable means and roll I may servemerely as a smoothing means or application of coating to side A may beomitted in which event jet I I would serve merely to hold the webagainst the smoothing roll 7. Roll 1 may rotate in a direction oppositeto the direction of the web travel or it may rotate in the samedirection but with a peripheral speed different from the lineal speed ofthe web.

According to the modification of the invention shown in Fig. 2. a web Iwith sides A and B is passed between squeeze rolls "5 and I8 which leavea limited quantity of fluid coating composition on both sides of theweb. The coating composition is supplied to side A by roll l6 whichturns in vat containing the coating mixture.

Coating composition is supplied to side B by ipe l9, near the entranceto the nip between l6 and I8. The web is carried past air-nozzle 20which emits a rectilinear substantially non-divergent air jet thatsmooths the coating on side A, preferably removing the excess therefrom,and that I likewise pushes the sheet into firm contact with the rigidblade or scraper 2|. Blade 2| smooths the coating on side B, preferablyremoving excess coating therefrom, and likewise serves to support theweb while the air jet from 20acts thereon. The web, coated and smoothedon both sides, is then dried and finished in any conventional way.

In this modification it is apparent that if coating is not applied toside A, the jet 20 will serve merely to hold the web against the scraper2| while it serves to smooththe coating on side B. It is likewiseapparent that rolls l6 and I8 may be replaced by any other suitablemeans for appurpose, 1. e. to support the web against the jet 20 and tosmooth coating on side B of the web. When a roll is used both, asapplicator and smoothing means as in the case of the roll 1 in Fig. 1,it is-preferre'd to use an air brush to spread the coating upon the saidroll. Nevertheless, in many cases fairly satisfactory results may beobtained by use of'a rigid doctor meana e. g., a blade or another roll,in place of the air brush it. The substitution of a roller, 1. e. theroller 23, for the air brush I is illustrated in Fig. 4.

a the roll I, making the web follow the contour of In the set-up shownin Fig. 1, the air jet from firmly against the rigid smoothing device.The latter function of the air brush is found to be very useful, even incases where the side of the web contacted by the air jet is not coated.The pressure of'the air jet pushes the web firmly against the opposedsmoothing means, making unnecessary extra tension to hold the sheet incontact with the smoothing means. The air jet makes it possible for theopposed smoothing means, to spread and smooth the coating satisfactorilyeven when the web makes substantially only a line contact with thesmoothing means. Thus may be avoided all frictional drag caused by asharp bend of the web about the smoothing means and contact of the webwith excessive area of the smoothing means.

The rigid smoothing means I in Fig. 1, or 2| in Fig. 2, likewise has twodistinct functions to fulfill. First it smooths the mobile coating onthe side of the web which it contacts; secondly it also serves as thesupporting means required to back up the web while the air brush isacting on the other side.

Thus it is seen that in either the arrangement of Fig. 1, orthearrangement of Fig. 2, there is double cooperation between the, airsmoothing means and the rigid smoothing means. For instance, air brushll of Fig. 1, and air brush 20 of Fig. 2, each has a primary functionand a secondary function, and coating-roll I of Fig. 1, and scraper 2|of Fig. 2, also each has a primary function and a secondary function.The primary function of each smoothing means, of course, is to smooththe coating on the side of the web on which it acts. Each means,however, is assisted in the accomplishment of its primary smoothingfunction, by the cooperating action of the opposed means as the latterperforms its secondary supporting function. Specifically, in Fig. 1, theair fromnozzle II has for its main purpose the smoothing of the coatingon side A of the web; the air jet isenabled to accomplish this purpose,however, only because of the support given by roll I on the oppositeside of the web. Conversely, coating roll 1 spreads and smooths thecoating on side B of the web as its chief function, but it is assistedin this action by the air pressure from nozzle H which pushes the webfirmly against roll I. 1

The particular arrangement of apparatus shown in-Fig. 1, produces apractical equivalent of a web coated and smoothed on both sides by theuse of an air brush. One of the outstanding advantages of the air brushmethod of coating is that a coating of uniform thickness can be appliedirrespective of considerable possible variation in thickness oruniformityof surface of the base stock. In the same way it is found thata uniform layer of coating composition can be spread upon the surface ofan applicator roll by use of an perfections in the roll itself. Hence auniform layer of coating may be spread on coating-roll I of Fig. 1, andthe coating may be transferred uni.- formly to a web contacting theroll, sincethe air jet from nozzle ll acts to push the web against theroll even if considerable variation in diameter may exist therein atvarious points along its length.

It will be seen that the invention makes possible the production in asingle operation of twoside] coated paper of the highest quality atspeeds comparable to those now used for making one-side coated papers.Besides this obvious advantage, it is believed that the fact that bothsides are coated before drying, makes the penetration of the coatingcomposition the same on both sides of the sheet, and tends to decreaselikelihood of trouble from curling of the finished sheet.

The invention likewise provides a new arrangement of apparatus,employing two air brushes, by which paper or other sheet material 1 maybe coated on both sides simultaneously. An

important feature of the invention is a method of holding a coated webagainst a rigid smoothing device by means of air pressure.

Iclaim:

- 1. A method of coating a web of fiexible'sheet material on both sidesin a single operation comprising continuously advancing the web;applying mobile coating composition to one side of the web, rigidlysupporting the reverse side of the web against a solid surface whilesubjecting the mobile coating on the first side directly opposite saidsurface to the action of a rectilinear, substantially non-divergent airstream, whereby the coating composition is spread and smoothed on saidfirst side; simultaneously applying mobile coating composition to thesurface and spreading and smoothing said coating thereon by means of asecond rectilinear, substantially n0n-diver gent air stream and movingthe surface in contact with the web whereby the layer of coatingthereon, is transferred to the second side of said web, and drying thecoated web.

2. A method of coating flexible webs on both sides comprisingcontinuously advancing the web, applying mobile coating composition tothe two sides of the web; substantially simultaneously smoothing thecoating on thetwo sides by subv jecting the coated web on one side tothe action of a rigid smoothing surface and on the other side to theaction of an air jet, the surface and the air jet being substantiallydirectly opposed to each other on opposite sides of the web, and dryingthe so-coated web.

3. In a method of smoothing mobile coating composition upon a flexibleweb by means of a rigid smoothing surface the improvement comprisingurging the web against said smoothing surface by means of an air jet.

4. A method of coating paper on both sides in which a paper web iscontinuously advanced, mobile coating composition is applied to the twosides of the web, the mobile coating composition is spread and smoothedsubstantially simultaneously on the two sides, on one side by an air jetand on the other by 3. rigid surface.

5. Apparatus for coating flexible sheet material comprising means forcontinuously advancing a web of the material, means for applying coatingto at least one side of the web, rigid means contacting said side of theweb for smoothing said air brush in spite of minor possible imcoating,and an air jet positioned to urge the web toward said smoothing means.

6. Apparatus as defined in claim 5 in which the smoothing means is ascraper.

7. Apparatus as defined in claim 5 in which the smoothing means is aroll.

8. Apparatus for coating a flexible sheet matev a free air jet.

10. Apparatus for coating flexible sheet material comprising means forcontinuously advanc ing a web 01' the material, means for applying,

coating to both sides of the web, rigid means contacting the web forsmoothing the coatin on one side thereof, and an air jet positioned tourge the web against said rigid means and also to smooth the coating onthe other side 0! the web.

11. Apparatus as defined in claim 10 in which the rigid smoothing meansis a scraper.

12. Apparatus as defined in claim 10 in which the rigid smoothing meansis a roller.

13. Apparatus for coating flexible sheet material comprisingmeans forcontinuously advancing a web of the material, a rotating rollercontacting one side of the web, means for applying coating to theroller, means for smoothing the coating on the roller, means forapplying coating to the other side of the web and an air iet positionedto urge the web against the roller and to smooth the coating on saidother side of the web.

14. Apparatus for coating flexible sheet material comprising means forcontinuously advancing a web of the material, a roller for applyingcoating to one side of the web and smoothing the coating thereon by awiping action and an air jet positioned to urge the web against saidroller.

STANLEY J. JOHNSON.

